When he was only 43, Peter Harrison had a severe heart attack that left him suffering from the symptoms of a damaged heart: shortness of breath, chest pain and increased risk of another heart attack. An otherwise healthy commercial real estate agent from Key Biscayne, Harrison was in and out of the hospital for 20 years treating his heart condition until last year when doctors at the University of Miami Miller School of Medicine injected his heart with stem cells as part of a study.